SHIFT WORK DISORDER - myCME.com

Median RT (msec)1600A140012001000800C6Slow Responses420Nights 5-7Nights 5-7Mathematical Processing****1600B140012001000800D6Night 8000:30 02:30 04:30 06:3000:30 02:30 04:30 06:30Time of Night Not Re-EntrainedTime of NightPartially Re-EntrainedCompletely Re-Entrained42Night 8*there was a significant main effect ofgroup on night shifts 5–7 [F 2,35= 4.14,P = 0.02]. The group that was not reentrainedhad significantly more slowresponses than the group that was partiallyre-entrained, but the differencebetween the not-entrained and completelyre-entrained groups did notreach statistical significance (P = 0.06)(panel A in Figure 5). There was a significantgroup × time-of-night interactionfor the number of slow responseson night shift 8 [F 3,39= 3.48, P = 0.04].Simple main effects showed that thesource of this interaction was significantlymore slow responses for the notre-entrained group compared to thepartially re-entrained group during the4:30 test bout (panel B in Figure 5).Figure 4—Median reaction time (top) and slow responses (bottom) on the mathematical processing task.Remaining aspects of figure as for Fig 2. Statistical symbols in panels A, B, and C denote a significantmain effect of group. *(P < 0.05) and **(P < 0.01) indicate differences between the not re-entrained andpartially re-entrained groups.significant group × time-of-night interaction during night shifts5–7 [F 6,108= 2.87, P = 0.02]. Simple main effects indicated thatthe not re-entrained group had significantly more slow responsesthan both the partially or completely re-entrained groups duringthe 2:30, 4:30, and 6:30 test bouts (panel C in Figure 3).There were no significant differences between the groups onnight shift 8 (panel D in Figure 3).Code Substitution TaskThere were no group differences inmedian RT (data not shown). However,the group that was not re-entrained hadmore slow responses (Figure 5, bottomrow). There was a significant group × time-of-night interactionon nights 5–7 [F 6,108= 2.78, P = 0.02]. The not re-entrainedgroup had significantly more slow responses than both the partiallyre-entrained and completely re-entrained groups duringthe 2:30, 4:30, and 6:30 test bouts (panel C in Figure 5). Therewere no significant group differences in the number of slowresponses on night shift 8 (panel D in Figure 5).Mathematical Processing TaskPerformance was better than during baseline for all 3 groups,but the partially and completely re-entrained group performedbetter than the not re-entrained group. Median RT was slowerin the not re-entrained group (Figure 4, top row). There wasa significant main effect of group during nights 5–7 [F 2,34=5.65, P < 0.01]. Post hoc tests indicated that the not re-entrainedgroup had significantly slower median RT than the partially reentrainedgroup (panel A in Figure 4). On night shift 8 there wasalso a significant main effect of group [F 1,12= 7.79, P = 0.02],indicating that the group that was not re-entrained had significantlyslower reaction times than the partially re-entrainedgroup (panel B in Figure 4).The number of slow responses was greater for subjects thatdid not achieve re-entrainment (Figure 4, bottom row). Onnights 5–7 there was a significant main effect of group [F 2,35= 8.25, P < 0.01]. The not re-entrained group had significantlymore slow responses than the partially re-entrained group (panelC in Figure 4). Slow responses on night shift 8 showed a similarpattern, but the main effect of group did not achieve statisticalsignificance [F 1,13= 3.92, P = 0.07] (panel D in Figure 4).Matching to Sample TaskMedian RT was close to baseline levels throughout thenight shifts, and there were no significant differences amongthe groups (data not shown). For the number of slow responsesMental Fatigue and Mood DisturbanceAll the groups began the night shifts with ratings of mentalfatigue and total mood disturbance that were relatively closeto their baseline levels (00:30 time points in Figure 6). Duringnight shifts 5–7 (Figure 6, left panels), mental fatigue and totalmood disturbance increased for all groups later in the nightshifts, but the partially and completely re-entrained groups remainedcloser to their baseline ratings late in the nights, whilethe group that was not re-entrained became more fatigued andhad greater mood disturbance. On night shift 8 (Figure 6, rightpanels), ratings for the partially re-entrained group remainedvery close to baseline levels, while the not re-entrained groupdemonstrated increased mental fatigue and mood disturbance,especially later in the night shift.On the mental fatigue scale for nights 5–7, there was a significantmain effect of group [F 2,36= 5.48, P < 0.01]. Post hoctests indicated that the not re-entrained group was significantlymore mentally fatigued than the partially and completely re-entrainedgroups (panel A in Figure 6). During night shift 8 therewas a main effect of group [F 1,14= 4.84, P = 0.045], indicatingthat the group that was not re-entrained was more mentallyfatigued than the group that achieved partial re-entrainment(panel B in Figure 6).Total mood disturbance was also higher for the group thatwas not re-entrained (Figure 6, bottom row). On night shifts5–7, there was a significant main effect of group [F 2,36= 4.12,SLEEP, Vol. 32, No. 11, 2009 1486Circadian Phase, Mood, Fatigue and Performance—Smith et al